The present invention relates to an embolization system to block flow through a selected portion of a lumen. More particularly, the present invention relates to a system for introducing occlusion particles into the lumen of a blood vessel.
Embolization techniques are currently used to treat a variety of vascular and non-vascular diseases. Such diseases include arteriovenous malformations (AVMs), aneurysms, arteriovenous fistulas, and tumors. There are currently three basic types of embolization systems in use. Those systems include embolic liquids, solid or solid-type agents, and particles.
Embolic liquids include glues, (polymerizing agents), alcohols, and precipitating agents. Typical examples of embolic liquids are n-butylcyanoacrylate (n-BCA), ethyl alcohol and a precipitating agent sold by Ethicon of Germany under the tradename Ethibloc. The glues used as embolic liquids typically act to polymerize and harden in the vessel, thereby blocking or occluding the vessel into which they are introduced. The alcohol or alcohol derivatives cause tissue damage to the vessel with resulting thrombus formation for occlusion. Precipitating agents typically include a precipitating agent which is dissolved in infusion solution, but insoluble in a blood environment. When the infusion solution is introduced into the vessel, the precipitating agent precipitates out to cause occlusion.
Embolic liquids currently suffer from a number of disadvantages. One disadvantage is that the liquids lack radiopacity. This makes it difficult to monitor the administration of the embolic liquids. Another disadvantage is that the release of embolic liquids into the vessel to be occluded is difficult to control. The liquids must be released upstream of the site at which eventual occlusion is desired. Blood flow carries the embolizing liquid through the lumen of the vessel, and it is difficult to control the release of a proper amount of occlusive liquid into the vessel to insure that occlusion occurs at the desired site in the vessel.
Solid agents, when used in an embolization system, conventionally include occluding articles which are more discrete in nature than embolic liquids. Such articles have typically been formed of suture material or coils which are introduced into the vessel. The suture material (often silk), once released, assumes a convoluted shape within the vessel to cause thrombus formation and occlusion. A suture material occlusion system is discussed in the Ritchart et al. U.S. Pat. No. 4,994,069 issued Feb. 19, 1991. Coils, or coil assemblies, used as solid occlusion agents are shown in the Sepetka U.S. Pat. No. 5,234,437 issued Aug. 10, 1993. The coils occlude the desired site in the vessel by posing a physical barrier to blood flow. This promotes thrombus formation at the desired site, which eventually occludes the vessel.
However, solid agents also suffer from a number of disadvantages. First, solid agents conventionally depend on thrombus formation in order to accomplish complete occlusion. However, if anticoagulant agents are introduced into the bloodstream during surgery, the anticoagulant can substantially prevent thrombus formation thereby minimizing the occlusive effect of the solid agent. Additionally, the bodies' natural clot dissolving factors can cause recanalization. Further, when the solid agent is a coil, it is either an insertion coil or a detachable coil. Insertion coils are introduced into the vessel by injection, or by being pushed through a base catheter. Once introduced into the vessel, they can become irretrievable and accurate delivery is difficult to control. When the coil is detachable, it must be particularly sized to fit the lumen of the vessel at the desired occlusion site. However, the size of the lumen of the vessel is difficult to predict. Therefore, it is not uncommon for the treating physician to move the solid agent (detachable coil) to the occlusion site only to find out that the dimensions of the detachable coil are inappropriate to the occlusion site in the vessel. This requires the physician to remove essentially the entire coil system and to re-insert the system with a different size detachable coil. It may be necessary to repeat this process a number of times before the properly sized solid agent is finally inserted in the lumen. Also, when removing an improperly sized detachable coil, it is not uncommon for the coil to engage the base catheter and unravel or unwind. Such a system is time consuming and inefficient.
A third conventional embolization system utilizes what are known as embolizing particles or occlusion particles. Embolizing particles are typically smaller than solid occlusion agents and are suspended in solution. The solution is injected into the lumen to be occluded through a catheter. Typical embolization particles are made of polyvinylalcohol (PVA). The polyvinylalcohol particles are formed of a ground block of material which is put through a series of sieves to segregate the particles into various size categories. The particles are suspended in solution and injected into the vessel through a delivery catheter.
However, conventional embolizing particles also suffer from a number of disadvantages. For example, in conventional systems, the particles cannot be easily retrieved once they are injected into the vessel. In addition, it is very difficult to control precisely how much of the injectate is delivered. Further, typical PVA particles are in suspension and are therefore not typically well aligned as they travel through the catheter. Therefore, they can wedge together and substantially block the delivery catheter. This requires the treating physician to either remove the entire system, including the delivery catheter, and replace it with another system, or to take extra time to remove the blockage from the delivery catheter. Another major problem associated with injecting PVA particles to occlude a vessel is referred to as reflux. Essentially, as PVA is injected into the vessel, and as the vessel begins to close, the distal flow at the occlusion site becomes smaller. Therefore, less injectate is needed at the occlusion site. If too much solution is injected, and the distal flow cannot accommodate the extra injectate, then the flow becomes proximal and can occlude a lumen of a normal vessel at a proximal site. This problem essentially arises from the difficulty in controlling the amount of PVA particles injected into the vessel.